This is an highly accurate clock & calender module as a Break-out Board (BoB). I use an RV3029-C2. C2 is a 5 mm SMD. The design is very simple. The PCB is 30 x 25 mm. It is based on an idea from Elektor 10/2014 page 57. In my case I have a backup battery. CLKOUT is used. My plan is to improve my project Humidity-controlled basement ventilation system. So I need an I2C bus and an interrupt signal with 1 Hz to poll the time. Here I use CLKOUT. The battery should last for ten years.
More than a half year up and running.... the accuracy is like a radio-controlled watch! Very good!
If you test this RTC with my project UART to I2C Converter via Attiny2313A please remove the 24C16 EEPROM because both (Clock and EEPROM) use the same I2C address.